1. Field of the Invention
The present invention relates to a storage medium, a storage method and a stored information reading method for use in storing and/or reproducing information performed in computers, electronic cameras, or the like, and, more particularly, to a storage medium, a storage method and a stored information reading method which can be suitably used when a high density apparatus or a large capacity apparatus is realized and which can be used in a wide temperature range.
2. Description of the Prior Art
Hitherto, a magnetic material has been usually used in an information storage method employed in a large-capacity storage apparatus.
The information storage method is disclosed in, for example, "Magnetic Material Ceramics" on P.143 (edited by Sakurai and Kannamaru, published by Ohm Co., Ltd. 1976).
A method in which an oxide is employed to serve as the above-described storage medium was disclosed in Japanese Patent Laid-Open No. 63-268087 in which a superconductor is used so as to record and/or reproduce information at a temperature lower than the critical temperature of superconductivity.
When the magnetic material is used in the above-described conventional technologies, the magnetized state of the magnetic material is utilized. Therefore, it has been considered that there is a limit in the storage portion density to about one storage portion per .mu.m.sup.2 due to the reduction of the magnetic domain and the intensity of the signal to be detected.
A storage method utilizing a superconducting oxide is a method in which superconducting state and a normal state of a perovskite oxide are arranged so as to respectively correspond to binary signals and the transfer between the superconducting state and the normal state is achieved by irradiations of hydrogen ions and oxygen ions. However, in the above described method, it is necessary to know whether a predetermined storage portion is in a superconducting state or normal state when reading information. Therefore, the storage medium must be maintained at temperatures below the critical temperature (Tc).
Since the critical temperature Tc in the case of an oxide can reach about 100K, cooling means such as a refrigerant for example liquid nitrogen or the like or a helium refrigerator is necessary. The necessity increases the size of the apparatus, creating a design and a limitation to arise when the apparatus is designed.
Since the transfer between the two states, superconducting state and the normal state, is utilized when information is recorded, the storage method utilizing the superconducting oxide can be used in only the binary digital recording apparatus. Therefore, it cannot be used in multi-valued recording apparatuses or analog recording apparatuses. Furthermore, since oxygen ions and hydrogen ions are used when information is recorded, a problem arises in that optical input signals such as video signals cannot be directly recorded.